L.J. Turbini, J. Schodorf, J. Jachim, L. Lach, R. Mellitz and F. Sledd
Today's emphasis on alternative flux technology as an approach to eliminate the use of chlorofluorocarbons (CFCs) requires an understanding of the corrosion potential of the new…
Abstract
Today's emphasis on alternative flux technology as an approach to eliminate the use of chlorofluorocarbons (CFCs) requires an understanding of the corrosion potential of the new fluxes. In 1989, Dr David Bono proposed that monitoring the effect of different soldering fluxes on the rate of corrosion of a copper wire printed on a circuit board would provide quantitative information on the corrosion potential of a flux. Further analysis of this testby Turbini et al. revealed that the degradation mechanism associated with Bono's test is the growth of conductive anodic filaments along the glass fibres of the epoxy‐glass boards. The original test method has been revised, and the test coupon redesigned with the goal of developing a standard, quantitative test method to characterise soldering fluxes. This paper will describe the equipment, test coupon and electrical circuitry associated with this proposed test method. Procedures chosen to reduce error sources associated with electrical noise will be reported and explained.
For a number of years electronic manufacturers of printed circuit assemblies have used rosin‐based soldering fluxes. Post‐solder cleaning was accomplished with chlorinated or…
Abstract
For a number of years electronic manufacturers of printed circuit assemblies have used rosin‐based soldering fluxes. Post‐solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are considering alternative cleaners for rosin flux or new flux choices which can be cleaned with water or left uncleaned. Many of the flux formulations are relatively new and their long‐term effect on the performance of products manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, there is no direct relationship between the total ionic level and the corrosivity of the soldering flux. Surface insulation resistance testing is used in the industry, but the results are misunderstood by many. This is due to the fact that SIR data represent a complex dependency on a number of factors including (1) the test conditions (temperature, humidity, bias), (2) the area of interactions (often referred to as the number of squares), (3) the separation between lines on the interdigitated comb pattern, (4) the presence or absence of bias voltage during the test and (5) the nature of the substrate. All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally reported by Dr David Bono, is being modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French UTE, will result in a new international standard. This paper reports the latest data on this important test development.
J. Guinet, X. Lambert and D. Bono
The corrosive power of solder pastes is studied by implementing a new method compatible with the common rules of use. The entire methodology is fully described. The results show…
Abstract
The corrosive power of solder pastes is studied by implementing a new method compatible with the common rules of use. The entire methodology is fully described. The results show evidence of corrosion with some solder pastes that have been identified by microscopic and EDX analysis. The corrosion mechanism is ‘mouse bite’ and conductive anodic filaments. A ranking of the different solder pastes tested is given and pass criteria for this new method of evaluation are proposed.
The 1980s and 1990s have seen the development of new andinteresting soldering flux formulations. Many of these fluxes exhibit improved solderingperformance or are favoured because…
Abstract
The 1980s and 1990s have seen the development of new and interesting soldering flux formulations. Many of these fluxes exhibit improved soldering performance or are favoured because of their reduced environmental impact. In order to further the understanding of these new fluxes and their interaction with the metallisation on the printed wiring board, as well as the substrate itself, one needs to examine test methods carefully and begin to correlate the data among the existing test methods. At Georgia Tech a variety of data have been collected on a number of fluxes including water soluble, low solids and activated rosin fluxes. Test methods for flux characterisation include surface insulation resistance testing, corrosion test measurements and recently impedance spectroscopy at low frequencies. This paper will review the variety of fluxes available, report on results of testing these fluxes using the techniques mentioned above and will define the important information related to soldering flux interactions which each test method uncovers.
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Surface insulation, electrochemical migration and various other insulation resistances are terms which are often glibly used, sometimes even incorrectly. This paper categorises…
Abstract
Surface insulation, electrochemical migration and various other insulation resistances are terms which are often glibly used, sometimes even incorrectly. This paper categorises different types of insulation resistance and catalogues about twenty practical applications of insulation resistance measurement, each with its ideal general conditions of measurement (test voltage, bias voltage, bias polarity, test voltage period, test frequency, test duration, temperature, humidity, test pattern type, test pattern dimensions, voltage gradients, tolerances, etc.) This description is independent of any of the nearly forty known, often contradictory, standards, most of which no longer correspond to the practical printed circuit or assembly of today. Also discussed are the different technologies of insulation resistance measurement, starting with the original non‐electronic ‘Megger®’ types through to modern laboratory electrometers and, finally, instrumentation specific to the practical measurement of printed circuit insulation resistances, including static and dynamic types. The importance of automatic statistical analyses is emphasised, especially with production testing as well as qualification procedures. This paper is aimed not only at those wishing to learn what modern insulation resistance testing is all about, but also at experienced persons wanting to marshall their thoughts about the fundamental meanings of insulation testing for different applications and specifications.
The need to use cleaning methods other than traditional CFC‐113 solvent for hi‐rel electronics imposes more rigid cleanliness testing. In the past, this was mainly limited to…
Abstract
The need to use cleaning methods other than traditional CFC‐113 solvent for hi‐rel electronics imposes more rigid cleanliness testing. In the past, this was mainly limited to ionic contamination control, but this is probably insufficient by itself when using other methods. This paper discusses the various methods for which instrumentation is available, from the practical standpoint. This should satisfy all the requirements of both procurement agencies and manufacturers. Particular emphasis is placed on the fact that most existing standards are out‐of‐date and should be urgently revised. It is suggested that the standards be based on statistically valid test results rather than the simpler, but risky, go/no‐go methods. These probability limit levels should be modulated according to the use to which the circuitry will be put and the technology used in its manufacture. Above all, emphasis is placed on testing methods that are more scientifically based with less empirical guesswork.